Statistics.Test.WilcoxonT

The Wilcoxon matched-pairs signed-rank test is non-parametric test which could be used to test whether two related samples have different means.

Wilcoxon signed-rank matched-pair test

Test

wilcoxonMatchedPairTest

Arguments

:: (Ord a, Num a, Unbox a)

=> PositionTest

Perform one-tailed test.

-> Vector (a, a)

Sample of pairs

-> Test ()

Return Nothing if the sample was too small to make a decision.

The Wilcoxon matched-pairs signed-rank test. The samples are zipped together: if one is longer than the other, both are truncated to the length of the shorter sample.

For one-tailed test it tests whether first sample is significantly greater than the second. For two-tailed it checks whether they significantly differ

Check wilcoxonMatchedPairSignedRank and wilcoxonMatchedPairSignificant for additional information.

Building blocks

wilcoxonMatchedPairSignedRank :: (Ord a, Num a, Unbox a) => Vector (a, a) -> (Int, Double, Double)

Calculate (n,T⁺,T⁻) values for both samples. Where n is reduced sample where equal pairs are removed.

wilcoxonMatchedPairSignificant

Arguments

:: PositionTest

How to compare two samples

-> PValue Double

The p-value at which to test (e.g. mkPValue 0.05)

-> (Int, Double, Double)

The (n,T⁺, T⁻) values from wilcoxonMatchedPairSignedRank.

-> Maybe TestResult

Return Nothing if the sample was too small to make a decision.

Tests whether a given result from a Wilcoxon signed-rank matched-pairs test is significant at the given level.

This function can perform a one-tailed or two-tailed test. If the first parameter to this function is TwoTailed, the test is performed two-tailed to check if the two samples differ significantly. If the first parameter is OneTailed, the check is performed one-tailed to decide whether the first sample (i.e. the first sample you passed to wilcoxonMatchedPairSignedRank) is greater than the second sample (i.e. the second sample you passed to wilcoxonMatchedPairSignedRank). If you wish to perform a one-tailed test in the opposite direction, you can either pass the parameters in a different order to wilcoxonMatchedPairSignedRank, or simply swap the values in the resulting pair before passing them to this function.

wilcoxonMatchedPairSignificance

Arguments

:: Int

The sample size

-> Double

The value of T for which you want the significance.

-> PValue Double

The significance (p-value).

Works out the significance level (p-value) of a T value, given a sample size and a T value from the Wilcoxon signed-rank matched-pairs test.

See the notes on wilcoxonCriticalValue for how this is calculated.

wilcoxonMatchedPairCriticalValue

Arguments

:: Int

The sample size

-> PValue Double

The p-value (e.g. mkPValue 0.05) for which you want the critical value.

-> Maybe Int

The critical value (of T), or Nothing if the sample is too small to make a decision.

Obtains the critical value of T to compare against, given a sample size and a p-value (significance level). Your T value must be less than or equal to the return of this function in order for the test to work out significant. If there is a Nothing return, the sample size is too small to make a decision.

wilcoxonSignificant tests the return value of wilcoxonMatchedPairSignedRank for you, so you should use wilcoxonSignificant for determining test results. However, this function is useful, for example, for generating lookup tables for Wilcoxon signed rank critical values.

The return values of this function are generated using the method detailed in the Mitic's paper. According to that paper, the results may differ from other published lookup tables, but (Mitic claims) the values obtained by this function will be the correct ones.

module Statistics.Test.Types

References

• "Critical Values for the Wilcoxon Signed Rank Statistic", Peter Mitic, The Mathematica Journal, volume 6, issue 3, 1996 (http://www.mathematica-journal.com/issue/v6i3/article/mitic/contents/63mitic.pdf)